U.S. patent application number 14/288464 was filed with the patent office on 2015-01-22 for vibration generation apparatus.
This patent application is currently assigned to DENSO CORPORATION. The applicant listed for this patent is DENSO CORPORATION. Invention is credited to Nobuyuki TAGUCHI, Takamoto WATANABE, Shigenori YAMAUCHI.
Application Number | 20150022277 14/288464 |
Document ID | / |
Family ID | 52343120 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150022277 |
Kind Code |
A1 |
YAMAUCHI; Shigenori ; et
al. |
January 22, 2015 |
VIBRATION GENERATION APPARATUS
Abstract
In a gyro sensor, a TDC detects a magnitude of vibration of a
vibrator. A drive circuit (excluding the TDC) determines a duty
ratio of a PWM drive signal in accordance with the magnitude of
vibration so that the magnitude of vibration becomes a
predetermined magnitude and outputs the PWM drive signal having the
determined duty ratio. The drive circuit (excluding the TDC)
includes a control circuit and a DCO. The control circuit measures
time corresponding to the control value by using a gate delay time,
generates the PWM drive signal having a pulse width corresponding
to the control value and outputs the PWM drive signal.
Inventors: |
YAMAUCHI; Shigenori;
(Nisshin-city, JP) ; WATANABE; Takamoto;
(Nagoya-city, JP) ; TAGUCHI; Nobuyuki;
(Nagoya-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO CORPORATION |
Kariya-city |
|
JP |
|
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
52343120 |
Appl. No.: |
14/288464 |
Filed: |
May 28, 2014 |
Current U.S.
Class: |
332/109 |
Current CPC
Class: |
G01C 19/5726 20130101;
H03K 7/08 20130101 |
Class at
Publication: |
332/109 |
International
Class: |
H03K 7/08 20060101
H03K007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2013 |
JP |
2013-148538 |
Claims
1. A vibration generation apparatus for driving a test body to
vibrate in response to a PWM drive signal, the vibration generation
apparatus comprising: a magnitude detection part for detecting a
magnitude of vibration of the test body; a drive part for
determining a duty ratio of the PWM drive signal in accordance with
the magnitude of vibration so that the magnitude of vibration
becomes a predetermined magnitude and outputting the PWM drive
signal having the determined duty ratio; wherein the drive part
includes a control circuit and a drive signal generation circuit,
the control circuit measuring time corresponding to the control
value by using a gate delay time, generating the PWM drive signal
having a pulse width corresponding to the control value, and
outputting the PWM drive signal.
2. The vibration generation apparatus according to claim 1,
wherein: the drive signal generation circuit generates the PWM
drive signal by using a pulse generated by a ring oscillator having
a plurality of gates connected in series in a ring form, the pulse
being generated based on the gate delay time, which indicates a
delay time of each gate.
3. The vibration generation apparatus according to claim 1, further
comprising: a phase difference detection part for detecting a phase
difference between a waveform phase of the PWM drive signal and a
vibration phase of the test body, wherein the drive part outputs a
phase-adjusted drive signal so that the phase difference becomes a
predetermined phase difference.
4. The vibration generation apparatus according to claim 3,
wherein: the phase difference detection part detects the phase
difference by using a pulse generated by a ring oscillator having a
plurality of gates connected in series in a ring form, the pulse
being generated based on the gate delay time, which indicates a
delay time of each gate.
5. The vibration generation apparatus according to claim 4,
wherein: the drive signal generation circuit uses the ring
oscillator, which the phase difference detection part uses, and
generates the PWM drive signal by using the pulse generated based
on the gate delay time provided by the ring oscillator.
6. The vibration generation apparatus according to claim 1,
wherein: the drive signal generation circuit generates, as the PWM
drive signal, a pulse, which corresponds to a waveform phase of the
PWM drive signal, and a pulse, which corresponds to the duty
ratio.
7. The vibration generation apparatus according to claim 6,
wherein: the drive signal generation circuit generates at least
eight pulses in one cycle period of change of the waveform phase.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese patent application No. 2013-148538 filed on Jul.
17, 2013.
FIELD
[0002] The present disclosure relates to a vibration generation
apparatus, which drives a test body to vibrate by a PWM drive
signal.
BACKGROUND
[0003] Various conventional systems include vibration generation
apparatuses, which drive a test body to vibrate by a PWM
(pulse-width modulation) drive signal. Some of the vibration
generation apparatuses generate PWM drive signals by comparing an
input signal level with a threshold level as disclosed in
JP-A-2005-524077 (US2003/0200803 A1), for example.
[0004] According to the vibration generation apparatus described
above, however, an analog waveform is utilized in comparing the
input signal level with the threshold level. The analog signal is
likely to be susceptible to noise or the like. If a circuit is
provided to reduce influence of noise, the apparatus becomes
large-sized.
SUMMARY
[0005] It is therefore an object to provide a vibration generation
apparatus, which reduces influence of noise in driving a test body
to vibrate by a PWM drive signal.
[0006] According to one aspect, a vibration generation apparatus is
provided for driving a test body to vibrate in response to a PWM
drive signal. The vibration generation apparatus comprises a
magnitude detection part for detecting a magnitude of vibration of
the test body, and a drive part for determining a duty ratio of the
PWM drive signal in accordance with the magnitude of vibration so
that the magnitude of vibration becomes a predetermined magnitude
and outputting the PWM drive signal having the determined duty
ratio. The drive part includes a control circuit and a drive signal
generation circuit. The control circuit measures time corresponding
to the control value by using a gate delay time, generates the PWM
drive signal having a pulse width corresponding to the control
value and outputs the PWM drive signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram showing a gyro sensor;
[0008] FIG. 2 is a plan view of one example of an element shown in
FIG. 1;
[0009] FIG. 3 is a waveform diagram showing signal components of a
displacement detection signal when the element is in a resonance
state;
[0010] FIG. 4 is an explanatory diagram showing a synchronous
detector circuit shown in FIG. 1;
[0011] FIG. 5 is a detailed diagram of a drive circuit shown in
FIG. 1;
[0012] FIG. 6 is a flowchart showing initial processing performed
by a control circuit shown in FIG. 5;
[0013] FIG. 7 is a flowchart showing AGC processing performed by
the control circuit;
[0014] FIG. 8 is a waveform diagram showing in detail a drive
detection signal at the AGC processing time;
[0015] FIG. 9 is an explanatory diagram showing a method of
generation of a PWM drive signal by a DCO shown in FIG. 5;
[0016] FIGS. 10A, 10B and 10C are schematic views of a vibration
body and electrodes, a waveform diagram showing one example of the
PWM drive signal, and a waveform diagram showing coupling noise,
respectively; and
[0017] FIGS. 11A and 11B are graphs showing effects of the AGC
processing on a duty ratio and an amplitude, respectively.
DETAILED DESCRIPTION OF THE EMBODIMENT
[0018] Referring to FIG. 1, a gyro sensor 1 is configured as a
vibration generation apparatus for vibrating a test body, that is,
driving the test body to vibrate by applying a PWM (pulse-width
modulation) drive signal thereto. The gyro sensor 1 is formed of an
element 10, two initial stage circuits 20, a signal detection
circuit 30, an EPROM 40 and a drive circuit 50. The element 10, the
initial stage circuit 20, the signal detection circuit 30 and the
EPROM 40 are conventional as used in general gyro sensors. The
drive circuit 50 and the initial stage circuit 20 form a
self-excited resonant circuit.
[0019] In the element 10, a vibrator 11 shown in FIG. 2 displaces
to deviate from the direction of vibration in response to external
force applied thereto while vibrating. As a result, the
electrostatic capacitance varies. The element 10, which is
exemplarily shown in FIG. 2 is conventional as used in MEMS
gyros.
[0020] The element 10 is formed of the vibrator 11, electrodes 12,
13, 14 and a frame 15. The vibrator 11 is supported by the frame
15. When a PWM drive signal is applied to the electrodes 13, 14,
electrostatic capacitance is generated between capacitive parts 13a
and 14a. This capacitance vibrates the frame 15 in the up-down
direction in FIG. 2.
[0021] The vibrator 11 vibrates with the frame 15. When external
force is applied, the vibrator 11 displaces in the left-right
direction in FIG. 2 and varies the electrostatic capacitance
between the vibrator 11 and the electrode 12. The element 10
outputs to the initial stage circuit 20 the electrostatic
capacitance between the capacitive parts 13a and 14a and the
electrostatic capacitance between the vibrator 11 and the electrode
12.
[0022] Referring back to FIG. 1, the initial stage circuit 20
includes a CV conversion circuit (not shown). This CV conversion
circuit converts the electrostatic capacitance to a voltage signal.
The initial stage circuit 20 on the signal detection side, which is
connected to the signal detection circuit 30, converts the
electrostatic capacitance generated between the vibrator 11 and the
electrode 12 to a voltage signal. This voltage signal is an angular
velocity signal, on which a voltage variation signal is
superimposed. The angular velocity signal indicates an angular
velocity of the vibrator 11 of the element 10. The voltage
variation signal is generated by the resonance of the element 10.
The initial stage circuit 20 on the drive side, which is connected
to the drive circuit 50, converts the electrostatic capacitance
generated between the capacitive parts 13a and 14a to a voltage
signal. In the following description, the voltage signal outputted
from the initial stage circuit 20 on the drive side is referred to
as a drive detection signal and the drive signal outputted from the
initial stage circuit 20 on the signal detection side is referred
to as a displacement detection signal.
[0023] The signal detection circuit 30 extracts the angular
velocity signal from the displacement detection signal inputted
from the initial stage circuit 20 to provide an output indicative
of behavior of the vibrator 11. The signal detection circuit 30
includes a synchronous detector 31, a LPF (low-pass filter) 32 and
an amplification adjust circuit 33. The drive signal generated by
the drive circuit 50 is inputted to the synchronous detector 31 as
a reference signal. The synchronous detector 31 performs
synchronous detection by using the reference signal thereby to
remove signal components of a drive signal period from the
displacement detection signal.
[0024] As shown in FIG. 3, the displacement detection signal is
separated into the angular velocity signal, the drive signal
component and a DC component (direct current component). It is
known in the art that a phase of an output signal of the element
deviates about 90.degree. relative to external force applied to the
element in a resonance state. In an example shown in FIG. 3 as
well, the drive signal component, which is the output signal
component generated when the vibrator 11 vibrates in response to
the drive signal, is 90.degree. out of phase relative to the drive
signal inputted as the reference signal.
[0025] For this reason, the synchronous detector 31 multiplies the
displacement detection signal and the reference signal as shown in
FIG. 4. Thus the drive signal component, which has the phase
deviation of about 90.degree. relative to the reference signal, is
removed from the displacement detection signal.
[0026] Referring back to FIG. 3, the signal detected by the
synchronous detector 31 is subjected to removal of high frequency
components by the LPF 32 and then to sensitivity correction and
signal amplification by the amplification adjustment part 33. A
sensitivity correction coefficient is stored in the EPROM 40.
[0027] The configuration of the drive circuit 50 will be described
next. As shown in FIG. 5, the drive circuit 50 includes a
time-to-digital converter (TDC) 51, a digitally-controlled
oscillator (DCO) 53, the control circuit 52, a switch 56, a time
A/D converter (ADC(TAD)) 57 and a ring oscillator 60. The control
circuit 52 may be a microcomputer, which performs various
programmed processing.
[0028] The ring oscillator 60 is a digital oscillation circuit.
This ring oscillator 60 may be configured as disclosed in, for
example, JP-A-H07-183800 (U.S. Pat. No. 5,477,196 A). That is, the
ring oscillator 60 includes a plurality of gate circuits 62 such as
inverters connected in a ring form so that an input signal (Pin)
inputted as a pulse signal is inverted by each gate circuit 62 and
circulated to return to the gate circuit 62, to which the input
signal is inputted. From a plurality of output terminals Q1 to QN,
each of which corresponds to each gate circuit 62, signals, each of
which corresponds to an inversion operation time (gate delay time)
of the gate circuit 62, are outputted. The signals outputted from
the plural output terminals Q1 to QN are inputted to the TDC 51 and
the DCO 53. The drive detection signal is inputted to the TDC 51
from the initial stage circuit 20. The drive signal is fed back
from the DCO 53 and inputted to the TDC 51. The TDC 51 detects the
phase difference of the drive detection signal relative to the
drive signal (that is, phase delay of the drive detection signal
relative to the drive signal) as digital time information.
[0029] This phase difference is detected by measuring a time
difference from a pulse rise time of the drive signal to a pulse
rise time of the drive detection signal (rise time of a signal
produced by digitizing the drive detection signal by a comparator
or the like). In measuring the time difference, the TDC 51 uses the
pulse signal generated by the ring oscillator 60 as a clock pulse.
That is, the TDC 51 counts the pulse signal, which is generated by
the ring oscillator 60 during a period from the pulse rise time of
the drive signal to the pulse rise time of the drive detection
signal, and calculates the phase difference based on the count
value.
[0030] The DCO 53 outputs the drive signal at an interval
corresponding to a control signal inputted from the control circuit
52. In determining the interval, the DCO 53 uses the pulse signal
generated by the ring oscillator 60 as a clock pulse. The drive
signal outputted by the DCO 53 is inputted to the element 10 and
also to the TDC 51. The DCO 53 may be configured as disclosed in
JP-A-H07-106923 (U.S. Pat. No. 5,525,939 A). Use of the clock pulse
of the same ring oscillator 60 is conventional as disclosed in
JP-A-H07-183800 (U.S. Pat. No. 5,477,196 A) and the like and hence
detailed description is not made here.
[0031] The control circuit 52 controls the interval of the drive
signal (that is, frequency of the drive signal) so that the phase
difference detected by the TDC 51 becomes a predetermined resonant
phase difference. This control is performed by outputting the
control signal, which is a digital signal, to the DCO 53. The
resonant phase difference means a phase difference between a phase
of the external force and a phase of vibration of an object in a
state that the object is in resonance. It is known that this
resonant phase difference is about 90.degree.. However this
resonant phase difference may deviate slightly from 90.degree. due
to various conditions. The resonant phase difference is, for
example, 87.degree. as a specific value.
[0032] The control circuit 52 controls the frequency of the drive
signal, because it is known that the deviation of the vibration
phase of the vibrator 11 (phase of the drive detection signal)
relative to the phase of the external force inputted to the
vibrator 11 (phase of the drive signal) depends on the frequency.
Specifically, in a case that the frequency is lower than the
resonant frequency, the phase delay of the vibration phase of the
vibrator relative to the phase of the external force becomes
smaller than the resonant phase difference, which is about
90.degree.. In a case that the frequency is higher than the
resonant frequency, the phase delay of the vibration phase of the
vibrator relative to the phase of the external force becomes larger
than the resonant phase difference. For this reason, the detected
phase difference can be adjusted by increasing or decreasing the
frequency of the drive signal. It is noted that, in a case that the
phase delay is smaller and larger than the resonant phase
difference, the two phases are in-phase and anti-phase,
respectively.
[0033] Since the detected phase difference can be adjusted by thus
increasing and decreasing the frequency of the drive signal, the
control circuit 52 performs frequency adjustment processing as
described later. That is, the frequency is increased when the
detected phase difference is smaller than the resonant phase
difference. Thus the detected phase difference becomes larger and
approaches the resonant phase difference. On the contrary, the
frequency is decreased when the detected phase difference is larger
than the resonant phase difference. Thus the detected phase
difference becomes smaller and approaches the resonant phase
difference.
[0034] The switch 56 selects either one of the drive detection
signal and two kinds of reference voltages in response to a select
signal outputted by the control circuit 52 and outputs the selected
signal to the ADC 57. The ADC 57 is formed as an ADC of a variable
input power voltage type and includes a plurality of gate circuits
62 similarly to the ring oscillator 60 described above. The ADC 57
outputs a count value corresponding to a voltage (input voltage) of
the drive detection signal as a digital value in accordance with a
sampling signal outputted from the control circuit 52. The ADC 57
thus operates as a time A/D converter (TAD).
[0035] The TAD is conventional and not described in detail here. In
the ADC 57, the drive detection signal (Sin) is inputted as a power
voltage of each gate circuit 62 through a buffer 61. The inversion
operation time in each gate circuit 62 varies with a voltage level
of the drive detection signal. Signals outputted from the plural
output terminals Q1 to QN are inputted to the control circuit
52.
[0036] The control circuit 52 performs, before the above-described
frequency adjustment processing, initial processing, which is
general resonance control processing, so that the vibrator 11 of
the element 10 is driven to general resonance state. The initial
processing of the control circuit 52 is performed in the initial
operation as shown in FIG. 6 at the time of starting measurement,
for example. The drive detection signal does not contain the
angular velocity signal component and hence the phase of the drive
detection signal is considered to be a signal originating from the
drive signal component.
[0037] In the initial processing, the general resonance control
processing described above is executed first (S1, S2). That is, the
drive signal outputted from the DCO 53 is swept (S1). Sweeping
covers a range from a frequency sufficiently lower than the
resonant frequency of the element 10 to a frequency sufficiently
higher than the resonant frequency. Sweeping the frequency is
finished at a time point when it is determined to be the general
resonance state. In a case that the ring oscillator 60 includes
gate delay circuits, the ring oscillator 60 has temperature
characteristics. For this reason, at S1, temperature compensation
is performed so that the frequency of the drive signal is swept
from the lowest limit to the highest limit irrespective of ambient
temperatures.
[0038] Subsequently, it is determined that the vibrator 11 of the
element 10 is in the general resonance state. Specifically, the
vibrator 10 is determined to be in the general resonance state when
the phase difference detected by the TDC 51 is within a
predetermined general resonance range, which is considered to
correspond to the general resonance state. The general resonance
range is, for example, from 90% to 110% of the resonant phase
difference. When the general resonance state is established in the
course of sweeping the frequency of the drive signal, an amplitude
of a waveform of the drive detection signal becomes large rapidly.
For this reason, in a case that the A/D converter (ADC 57 or the
like) is provided for converting the drive detection signal to a
digital signal, the general resonance state may be determined based
on the amplitude of a signal outputted from the A/D converter. S3
is executed after determination of the general resonance state.
[0039] Subsequently, the frequency adjustment processing described
above is executed. That is, the phase difference between the drive
signal and the drive detection signal is detected. Specifically, a
signal indicating the phase difference is taken out from the TDC
51.
[0040] Then the frequency of the drive signal is changed so that
the detected phase difference match the resonant phase difference
(S4). Specifically, when the detected phase difference is smaller
and larger than the resonant phase difference, the frequency of the
drive signal is increased and decreased by a predetermined value,
respectively. After changing the frequency of the drive signal, S3
is executed to detect the phase difference again.
[0041] When it is determined that the detected phase difference
equals the resonant phase difference, the frequency is not changed.
When the frequency is not changed, S3 may be executed again to
continue monitoring of the phase difference. Alternatively, the
initial processing of FIG. 6 may be finished. When the initial
processing is finished, the self-excited resonance state of the
vibrator 11 is maintained by continuing the processing
corresponding to S3 and S4 while detecting the angular velocity
signal component.
[0042] The control circuit 52 performs AGC (automatic gain control)
processing shown in FIG. 7 separately from the initial processing
shown in FIG. 6. The
[0043] AGC processing is started at every predetermined interval or
at every change of the ambient temperature in excess of a
predetermined reference value of change. This processing is for
controlling the duty ratio of the PWM drive signal so that the
magnitude of vibration of the vibrator 11 is maintained at a
predetermined magnitude level. In S11 to S13, the processing of the
A/D conversion is continued for a period set for each
processing.
[0044] In the AGC processing, as shown in FIG. 7, the reference
voltage of 1.6V is A/D-converted first (S11). In this step, a
select signal, which indicates an input of the first reference
voltage (1.6V), is outputted to the switch 56 so that the first
reference voltage is inputted to the ADC 57 through the switch
56.
[0045] The control circuit 52 also has a configuration of the
synchronous detection similarly to the synchronous detector 31. The
control circuit 52 is configured to synchronously detect the drive
signal and the drive detection signal so that the vibration phase
of the vibrator 11 is detected. The control circuit 52 outputs a
sampling signal to the ADC 57 at time points when the vibration
phase becomes 0.degree. and 180.degree., that is, at every interval
of 1/2 cycle period. The ADC 57 outputs the digital value based on
the count value of the ring oscillator between two sampling
signals.
[0046] This digital value corresponds to integration of changes of
the voltage value between the sampling signals. The resolving power
is the gate delay time. The digital value at this time corresponds
to A shown in FIG. 8.
[0047] Subsequently, the drive detection signal Sin is
A/D-converted (S12). In this step, a selecting signal, which
indicates an input of the drive detection signal, is outputted to
the switch 56 so that the drive detection signal is inputted to the
ADC 57 through the switch 56. The ADC 57 thus outputs a digital
value, which corresponds to an average voltage thereof at every 1/2
cycle period of the drive detection signal. That is, the digital
value at this time becomes a value, which is averaged at every 1/2
cycle period of the drive detection signal. This digital value
corresponds to B and C shown in FIG. 8.
[0048] Subsequently, the reference voltage of 1.2V is A/D-converted
(S13). In this step, a selecting signal, which indicates an input
of the second reference voltage (1.2V), is outputted to the switch
56 so that the second reference voltage is inputted to the ADC 57
through the switch 56. The ADC 57 thus outputs a digital value,
which corresponds to D shown in FIG. 8.
[0049] In the flowchart shown in FIG. 7, the first reference
voltage (1.6V), the drive detection signal and the second reference
voltage (1.2V) are sampled in this order. In the example of FIG. 8,
however, the first reference voltage (1.6V), the second reference
voltage (1.2V) and the drive detection signal are sampled in this
order. This order of sampling may be arbitrarily determined.
[0050] Subsequently, a ratio ABC/LAD of a difference of potentials
in the drive detection signal (potential difference ABC between B
and C in FIG. 8) to a difference of potentials of the reference
voltage (potential difference LAD between A and D in FIG. 8) is
calculated (S14). Then the duty ratio of the PWM drive signal is
set so that the calculated ratio is maintained at a constant value.
The potential difference of the drive detection signal, which is
smaller than a target value, indicates that the magnitude of
vibration of the vibrator 11 is smaller than the target value.
Therefore, the duty ratio is set to increase the magnitude of the
frame 15. The potential difference of the drive detection signal,
which is larger than the value of the target ratio, indicates that
the magnitude of vibration of the vibrator 11 is larger than the
target value. Therefore, the duty ratio is set to decrease the
magnitude of vibration.
[0051] The control circuit 52 calculates, at S14, a count value DT
of the ring oscillator 60, which corresponds to 1/8 period of the
vibration period of the vibrator 11, so that the phase difference
between the drive signal and the drive detection signal becomes the
resonant phase difference. The control circuit 52 calculates a
value .alpha., with which the duty ratio for making the ratio
between the potential difference of the drive detection signal and
the potential difference of the reference voltage constant becomes
(DT-.alpha.)/DT. The control circuit 52 thus outputs eight values
to the DCO 53 in one cycle period. Those values are outputted in
the order of (DT-.alpha.), (DT-.alpha.), (DT+.alpha.),
(DT+.alpha.), (DT-.alpha.), (DT-.alpha.), (DT+.alpha.),
(DT+.alpha.) and the like.
[0052] As shown in FIG. 9, the DCO 53 outputs to the electrode 13,
for example, the low level signal, which is lower than the
potential of the reference signal, as the first two output signals
(pulses). The DCO 53 outputs the reference signal of the reference
potential as the next two output signals. The DCO 53 outputs the
high level signal, which is higher than the potential of the
reference signal, as the further next two output signals. The DCO
53 outputs the reference signal as the last two output signals.
[0053] The DCO 53 generates, in response to the above-described
output signals from the control circuit 52, the PWM drive signal by
continuously outputting the signal of each level for a period,
which corresponds to the count value ((DT-.alpha.) or (DT+.alpha.))
of the ring oscillator 60 designated by the control circuit 52.
This configuration outputs the pulse (even-numbered pulse), which
corresponds to the vibration phase, and the pulse (odd-numbered
pulse), which corresponds to the duty ratio. The DCO 53 thus
outputs at least eight pulses in one cycle period of change of the
waveform phase (vibration phase).
[0054] The drive circuit 50 (DCO 53) applies a first PWM drive
signal shown in FIG. 9 to one electrode (first electrode) 13 of the
pair of electrodes 13, 14 (FIG. 10A), to which the PWM drive signal
is applied to vibrate the vibrator 11. The drive circuit 50 also
applies a second PWM drive signal to the other electrode (second
electrode) 14. The second PWM drive signal is of opposite polarity
to the first PWM drive signal. That is, as shown in FIG. 10B, when
the high level signal is being applied to the first electrode 13,
the low level signal is being applied to the second electrode 14.
Both of the first PWM drive signal and the second PWM drive signal
takes a reference potential level of the reference signal between
the high level signal and the low level signal. Thus coupling noise
is reduced as shown in FIG. 10C. The AGC processing is finished
when the signals are outputted as described above.
[0055] The above-described embodiment has the following features
and advantages.
[0056] The gyro sensor 1 has a pair of electrodes 13 and 14, to
which the PWM drive signal is applied in the vibrator; and the
drive circuit 50, which outputs, as the PWM drive signal, the high
level signal and the low level signal to the pair of electrodes 13
and 14. The high level signal and the low level signal have
potentials higher and lower than the potential of the reference
signal, respectively. The drive circuit 50 outputs the high level
signal and the low level signal to one and the other of the pair of
electrodes 13 and 14, respectively. Since the high level signal and
the low level signal are outputted to the pair of electrodes 13 and
14, noises generated by those signals can be cancelled. As a
result, influence of noise can be reduced.
[0057] The gyro sensor 1 has the TDC 51 (including the ring
oscillator 60), which detects the phase difference between the
waveform phase of the PWM drive signal and the vibration phase of
the vibrator 11. The dive circuit 50 (excluding the TDC 51) outputs
the phase-adjusted drive signal so that the phase difference
becomes the predetermined phase difference. The phase difference
between the waveform phase of the PWM drive signal and the
vibration phase of the vibrator 11 can be controlled to the
predetermined phase difference.
[0058] Further, since the TDC 51 outputs the digital value
corresponding to the phase difference, more anti-noise performance
can be provided.
[0059] The drive circuit 50 (excluding the TDC 51) outputs the
phase-adjusted drive signal so that the phase difference between
the waveform phase of the PWM drive signal and the vibration phase
of the vibrator 11 becomes the phase difference, which causes the
self-excited resonance of the vibrator 11. Since the vibrator 11
resonates by self-excitation, the energy supplied to the vibrator
11 can be minimized and the vibrator 11 can be driven to vibrate
efficiently.
[0060] The drive circuit 50 (excluding the TDC 51) outputs the
phase-adjusted drive signal so that the vibration phase has a phase
delay of 90.degree. or about 90.degree. relative to the waveform
phase. The vibrator 11 can be driven to resonate by
self-excitation.
[0061] The TDC 51 detects the phase difference based on the gate
delay time of the ring oscillator 60, in which the plurality of
gate circuits 62 are connected in series in the ring form. The gate
delay time indicates the delay time of each gate. Since the phase
difference can be detected with the resolving power of the gate
delay time, the accuracy of the phase difference detection can be
increased.
[0062] The signal detection circuit is provided for producing the
output based on the behavior of the vibrator 11. Since the output
value is provided in correspondence to the behavior of the vibrator
11 (for example, Coriolis force applied to the vibrator 11), the
gyro sensor 1 can be used to function as a sensor.
[0063] The TDC 51 detects the magnitude of vibration of the
vibrator 11. The drive circuit 50 (excluding the TDC 51) determines
the duty ratio of the PWM drive signal so that the magnitude
becomes the predetermined magnitude in accordance with the
magnitude of vibration of the vibrator 11. The drive circuit 50
outputs the PWM drive signal of the determined duty ratio. The
drive circuit 50 (excluding the TDC 51) includes the control
circuit 52 and the DCO 53. The control circuit 52 outputs the
control value corresponding to the target duty ratio of the PWM
drive signal. The DCO 53 generates the PWM drive signal, which has
the pulse width corresponding to the inputted control value and
generates the PWM drive signal, by performing time measurement
based on the gate delay time in accordance with the control value.
Since the PWM drive signal having the pulse width corresponding to
the inputted control value is generated by measuring time based on
the gate delay time, the processing of generating the PWM drive
signal can be performed by digital processing. As a result, in
comparison to the case of generation of the PWM drive signal by
analog processing, influence of noise can be reduced.
[0064] The DCO 53 generates the PWM drive signal by using the pulse
generated by the ring oscillator 60 having the plurality of gate
circuits 62 connected in series in the ring form. The pulse is
generated based on the gate delay time, which indicates the delay
time of each gate circuit 62. Since the PWM drive signal having the
pulse width, the resolving power of which is the gate delay time,
the PWM drive signal can be outputted with higher accuracy.
[0065] The DCO 53 uses the same ring oscillator 60 as the TDC 51
(ring oscillator 60) uses and generates the PWM drive signal by
using the pulse generated based on the gate delay time provided by
the ring oscillator 60. The DCO 53 and the TDC 51 (ring oscillator
60) can have the common resolving power. The signal processing can
be simplified.
[0066] The DCO 53 outputs, as the PWM drive signal, the pulse
corresponding to the waveform phase and the pulse corresponding to
the duty ratio. The phase of the drive signal can be outputted by
the pulse corresponding to the waveform phase in outputting the PWM
drive signal.
[0067] The DCO 53 outputs the pulses at least eight times in the
period, in which the waveform phase changes one cycle period. The
PWM drive signal can be generated while outputting the signal
indicating the phase of the drive signal appropriately.
[0068] The ADC 57 generates not only the amplitude digital value
corresponding to the magnitude of the vibration waveform of the
vibrator 11 but also the voltage digital value corresponding to the
difference between the two different reference voltages. The drive
circuit 50 (excluding TDC 51) generates the drive signal so that
the ratio between the voltage digital value and the amplitude
digital value becomes constant. Since the amplitude of the
vibration waveform can be processed digitally, influence of noise
can be reduced in comparison to the configuration of analog
processing. Since the drive signal is generated so that the ratio
between the difference (voltage digital value) of the reference
voltages and the amplitude digital value corresponding to the
magnitude of the vibration waveform is maintained constant, the
drive signal can be generated appropriately even in a case that the
configuration for A/D conversion is affected by the environmental
condition such as temperature.
[0069] FIGS. 11A and 11B shows a result of comparison between a
case (AGC) that the AGC processing is performed as in the present
embodiment and a case (NO AGC) that no AGC processing is performed.
It is understood that, in the case of no AGC processing, the duty
ratio of the PWM drive signal is not changed from the constant
value (FIG. 11A) but the amplitude of the drive detection signal is
varied in accordance with temperature (FIG. 11B). In the case of
AGC processing as in the present embodiment, the duty ratio of the
PWM drive signal is feedback-controlled in accordance with the
amplitude of the drive detection signal. As a result, the duty
ratio of the PWM drive signal varies with temperature (FIG. 11A)
and the amplitude of the drive detection signal remains to be
constant.
[0070] The ADC 57 detects an average value of the vibration
waveform in a former half period of the waveform and an average
value of the same in a latter half period and sets the difference
of these average values as the amplitude digital value. The
amplitude can thus be detected with high accuracy.
[0071] The ADC 57 is configured as the time A/D converter (which
outputs the input voltage as the digital value corresponding to the
gate delay time). The A/D conversion can be performed in simple
configuration. The ADC 57 sets the sampling time point by using the
synchronous detection. The sampling time point can be set more
accurately. The ADC 57 generates, at every regular interval or at
irregular interval, the voltage digital value corresponding to the
difference between the two different reference voltages. Since the
voltage digital value can be generated repetitively when necessary,
it is possible to respond flexibly to changes in the environmental
condition such as temperature.
[0072] The switch 56 is provided to select and output the vibration
waveform of the vibrator 11 or either one the reference voltages
and the ADC 57 integrates the inputted signal. The control circuit
52 (drive circuit 50) switches over the switch 56 at every
predetermined time point. The ADC 57 samples the vibration waveform
when the vibration waveform of the vibrator 11 is selected by the
switch 56. The ADC 57 samples the reference voltage when either one
of the reference voltages is selected by the switch 56. Since the
ADC 57 switches over the signal to be A/D-converted to the
reference voltage or the vibration waveform, the vibration waveform
can be detected while appropriately correcting this characteristics
even when the characteristics of the ADC 57 changes in accordance
with the environmental condition such as temperature.
[0073] The ADC 57 sequentially samples the one reference voltage
(high level), the vibration waveform and the other reference
voltage (low level) in this order. The vibration waveform can be
detected accurately even when the reference voltage has certain
variations.
[0074] The embodiment described above may be modified. For example,
in the AGC processing according to the embodiment, two reference
voltages (1.6V and 1.2V) are provided and the difference between
the two voltages is calculated. However, only one reference voltage
may be provided and a voltage such as an average voltage of the
drive detection signal (center voltage of the amplitude) may be
used as another reference voltage.
[0075] In the embodiment, the gyro sensor 1 corresponds to the
vibration generation apparatus and the vibrator 11 corresponds to
the test body. The drive circuit 50 (excluding TDC 51) corresponds
to a drive part, the TDC 51 and the ring oscillator 60 correspond
to a magnitude detection part. The TDC and the ring oscillator 60
corresponds to a phase difference detection part and the DCO 53
corresponds to a drive signal generation circuit.
* * * * *